1. Field of the Invention
The invention generally relates to systems and methods for modifying features in a semi-conductor device to enhance semi-conductor chip performance. More specifically, the invention relates to systems and methods that modify features within a common reticle field using a common exposure dose.
2. Related Art
Critical Dimension (CD) control, especially for FET transistor gate level or semiconductor devices are becoming more and more important as technology requirements are becoming more stringent. Using current lithographic techniques, including Optical Proximity Correction (OPC), model building and masks are increasingly difficult and expensive to build. Moreover, inherent variabilities in mask manufacturing processes exist that can exhibit themselves in inconsistent dimensions from device to device, or from region to region in a single device. Methods and systems rendering modifications to features already imparted to a device would thus prove a meaningful asset to the industry.
There are currently many sources for systematically varying linewidth features, for example, within a common reticle field of semiconductor devices. Exposure control, for example, results in the same doses of light being applied to resist throughout a full reticle field in current practices. Such dosing tends to increase or decrease all linewidths in the reticle field to the same degree however. Lower chip performance tends to occur as a result. Moreover, other means to vary or adjust linewidths, other features, or critical dimensions differently with a common reticle field tend to be more complex or more costly to implement than is ideally preferred.
More recently, as set forth in co-pending U.S. patent application Ser. No. 10/906,846 (IBM Ref.: BUR920040189US1), of common assignment herewith, double exposure techniques have been developed using a low transmission mask. In such double exposure techniques, different semiconductor features are modified at selected areas within the common reticle field by a second exposure dose that is transmitted to the photoresist through the low transmission mask. The modifications tend to be binary according to the features of the low transmission mask, wherein modified areas of the photoresist have been exposed to the dose through the low transmission mask and non-modified areas of photoresist are not exposed to the dose. While this technique tends to improve chip performance by modifying features within a common field, at least one additional mask and exposure would be required to vary features further within the common reticle field. Moreover, other systems and methods for modifying features within a common reticle field tend to be more complex or more costly, or both, than is preferred.
In view of the above, a need exists for systems and methods that modify features within a common reticle field during a common exposure dose in a simple and cost effective manner.